In one province alone, the utility pole companies remove from service approximately 20,000 distribution and 2000 transmission poles per year. At present, disposal practices include reuse by these companies, stockpiling, selling to landscapers and reuse by local farmers. The vast majority of the poles and crossarms (hereinafter referred to as poles) have been treated with pentachlorophenol (PCP) as a means of reducing decay and prolonging the life of the pole. The outer 2.5 centimeters of the pole is impregnated with a solution of 95% carrier oil and 5% PCP. While current legislation does not classify PCP-treated poles as hazardous waste, concern has been raised as to the possible future liability associated with used poles. If the outside material is safely removed and separated for recycling, the preservative-free interior wood can be reused and recycled.
Separation of mixed contaminated substances by means of heating in an oxygen-free environment is termed thermolysis or pyrolysis. Various thermolysis and pyrolysis processes have been developed and are available in the public domain. One type consists of a recirculating hot sand bed, while another comprises a non-circulating sand bed. These processes have the disadvantage of causing abrasive wear to various parts of the machinery and of contaminating the end products with sand particles. These devices have been used primarily for the conversion of wood products and agricultural waste to liquid oils and specialty chemicals.
Another device relies on the oblation of larger wood particles along the sides of a reactor. This device does not alow for the rapid heating of the wood, and hence the outcome is more difficult to predict.
It is an object of the present invention to have rapid heating of the preservative contaminated sawdust and rapid cooling and condensation of the gas without contamination of the clean sawdust by sand.
The present invention uses a fast thermolysis process to rapidly heat the contaminated wood and then rapidly condenses the vapourized wood preservatives to prevent secondary chemical reactions from occurring.
The applicant has conducted laboratory studies which are detailed below. These studies show that PCP can be removed from sawdust to less than natural backgound levels using thermolysis.